APPARATUS AND METHOD FOR MANUFACTURING A DOUBLE-SIDED EMBOSSING FIBROUS WEB AND SUCH DOUBLE-SIDED WEB

Abstract: An apparatus and a method for manufacture a double-sided three dimensional embossed web is provided. A web (15) is led through the nip between an embossing roller (18) and a pressure roller (19). The web (15) is preferably in a non-cured state and may be a paper or a plast web. If a pressure roller (19) having a smooth and hard surface is used, it has surprisingly created the effect of a double-sided three dimensional embossing. Such double-sided embossing gives the web a good hand and feel and a good drapability thereby making it suitable for manufacturing cloth, curtains, diapers and other products which should feel soft and pleasant and which should have a good drapability to be compared with that of knitwear and textiles. The embossed web would occur with the embossing or impressions (24) provided on two surfaces as a mirror image around a plane of symmetry (23) passing through the middle of the web (15). In the same way raised areas (26) would be opposed by raised areas (26).

Description: APPARATUS AND METHOD FOR MANUFACTURING A DOUBLE-SIDED EMBOSSING FIBROUS WEB AND SUCH DOUBLE-SIDED WEB This invention relates to an apparatus and a method for providing a fibrous web with embossings on both sides thereby creating a double-sided three dimensional embossed web. The fibers to be used in the present invention comprise cellulosic fibers, wood fibers, mixtures with synthetic fibers including bicomponent fibers and synthetic fibers. The synthetic fibers may e.g. be of polypropylene or polyethylene. Also glasfibers, rock wood fibers, and pretreated fibers may be used. The invention also relates to the fibrous web itself. The embossing process is an in¬ line process by which the web formed is led through a so-called embossing calendar. The web may be a plast web, a paper web or the like. It is also possible to emboss a multi-.ayer web. The embossing calendar comprises an embossing roller and a cooperating pressure roller between the web is led in order to emboss one side of the web. If a double-sided embossing is provided the web is led through a further embossing calendar having the embossing roller and the pressure roller arranged oppositely in relation to the positioning in the first embossing calendar. Thus the prior technique results in a volu¬ minous apparatus. It is connected with serious problems if the double-siαed embossing is effected simultaneously by the use of two embossing rollers. Thus a great risk exists that the web will be broken in areas where two raised portions are arranged opposite each other in a central plane passing through the axis of rotation for the two embossing rollers. This risk for breaking or rupturing the web is especially high when thin webs are embossed. For many products it is a desire to have double-sided embossed webs and it is desired that such web could be rather thin. When having double-sided embossing the web would have a high quality in hand and feel and also in drapability. Thus, a sheet being embossed only at one side would have a very poor drapability being governed by the non-embossed surface of the web. Moreover, a web being embossed only at one surface would feel more stiff and hard. Accordingly, it is said to have a poor hand and feel. When embossing the web at both sides, the web will a lot of points around which the web is able to bend. This is the effect which gives the web a good hand and feel and a good drapability. Such web is especially suitable for manufacturing cloths, cur¬ tains, wash cloths, diapers, and other products which should feel soft and pleasant for users or which should have a drapability to be compared with that of knitwear and textiles. The web may be manufactured with reinforcements nets, syntetic fibers included in the cellulosic fibers or be made solely of cellulosic fibers. It is the object of the present invention to provide a fibrous web having an embossing on both surfaces in order to provide a web having a good hand and feel and a good drapability, irrespective of the thickness of the web. According to the present invention the double-sided embossing of the fibrous web is provided simultaneously by leading the web in-between two rollers. One of said rollers is a embossing roller know per se and the other roller is a pressure roller being provided with a hard and smooth surface. Surprisingly it has been shown that the use of a hard and smooth pressure roller in contradiction to the well-known soft pressure roller creates the effect of a double-sided three dimensional embossing. Even after great consideration of this surprisingly effect the inventor has not been able to give a causal explanation. The embossings provided on the two surfaces of the web occur as a mirror image around a symmetri plane passing through the middle of the web. Thus, an impression at one side of the web would be opposed by an impression at the other side of the web. According to a preferred embodiment the second roller is made of a cronium-plated steel roller giving a very hard and smooth surface. Thereby an especially good and concise embossing is obtained on both sides. The two rollers used should be arranged with a mutual distance between the surfaces so that no nip effect would occur on the material of the web which is situated in front of indentations on the embossing roller. Thus it is preferred that the two rollers are set depending on the thickness of the web and the type of the web so that embossing only occurs in the material of the web which is situated in front of the raised areas of the embossing roller. The rollers used could have various dimensions. Thus the lenght could be between 3 and 4 meters and the diameter could be between 0.1 and 0.7 meters. The surface speed of the roller would be between 20 and 400 meters/minute and the rollers should preferably be heated to a temperature between 130°C and 400°C, preferably between 200 and 330°C. When providing embossings on both sides in the method according to the invention, it is possible to establish the web-manufacturing plant with an over-all size being less than by using conventional embossing methods requiring the use of two subsequent embossing calendars. The web produced would preferably be arranged with very short distances, e.g. less than 3 mm or even less than 2 mm between the raised areas in order to have as many bending points as possible. Further features and advantages of the present invention will be understood by reference to the attached drawings taken in conjunction with the ensuing discussion. DESCRIPTION OF THE DRAWINGS In the drawings, Fig. 1 shows a schematic side view of an apparatus according to the invention, Fig. 2 shows an enlarged view of an embossing roller, Fig. 3 shows a partial sectional view through a web made according to the present invention, and Fig. 4 shows a photography of a web according to the present invention. Fig. 1 illustrates schematically a plant for dry laying of paper. In Fig. 1 only main elements of the plant are illustrated. Thus in order to function the plant would require more elements such as binder supply means, a curing unit and means for conditioning the web formed. However, such elements are within the knowledge of the skilled in the art and a detailed explanation thereof will not be necessary for the understanding of the present invention which is related to the embossing. It is preferred to arrange the curing unit after the embossing rollers. However, it is also possible to arrange the curing unit before the embossing roller. The plant comprises a fiber distributor 1, a suction box 2 and an endless foraminous forming wire 3 passing therebetween. The endless forming wire 3 consists e.g. of a mesh net constructed using bronze wires. The forming wire 3 is supported on rollers 4 and is driven by suitable driving means (not shown) so that it will continously pass between the fiber distributor 1 and the suction box 2. The forming wire 3 moves in direction of an arrow 5. The suction box 2 comprises a suction pipe 6 which is connected to a fan (not shown) for creating a vacuum therein. The forming wire 3 passes through the nip of a pair of rollers 7,8. Thereby providing a compaction of the dry laid fibers is effected. An endless band 9 is arranged in continuation of the forming wire 3. The band 9 is driven in direction of an arrow 10. A further endless band 11 is provided above the forming wire 3 and a part of the endless band 9. The interior of the endless band 11 is divided into two compartments 13,14 having an overpressure and a vacuum, respectively. This arrangement is intended for transferring the fibrous web 15 formed from the forming wire 3 to the endless band 9. Spraying nozzles 16 are arranged above the fibrous web 15. The spraying nozzles 16 may be used to adjust the humidity of the web within limits between 5 and 10%, preferably within 7 to 8 % . This humidity is essential as problems otherwise may occur due to static electricity. It is possible to provide spraying nozzles corresponding to the nozzles 16 at the other side of the fibrous web 15. Before winding up -ne final fibrous web 15 onto a roller 17 the web 15 passes through the nip of the rollers 18,19. The rollers 18,19 constitute an embossing apparatus according to the invention. The roller 18 is provided with a pattern in its surface determining the form of the embossing of the web. The roller 19 which is a so-called pressure roller has a smooth and hard surface. The roller 19 is preferably made of a cronium-plated steel roller. Thus the pressure roller 19 is totally different from the pressure rollers, which are ordinarily used. These prior art rollers are based on the principle that they should have a soft and flexible surface which may yield when embossing the web. However, such known embossing apparatus allows only for an embossing on one surface of the web. In this respect it should be remembered that a one-sided embossed web would have a drapability being governed on the smooth side. As illustrated in Fig. 2 the roller 18 is provided with a pattern 20 comprising engraved areas 21 and raised areas 22. The rollers 18,19 is provided with a mutual distance so that the nip effect would occur in fibers situated in front of the raised areas 21 and so that no nip effect would occur in the fibers situated in front of the engraved areas 21. Thus there is a demand for a very precise positioning of the two rollers 18, 19. The apparatus according to the invention would work according to a method by which a double-sided three dimensional embossing is effected on the fibrous web 15. Such a double-sided embossed fibrous web is illustrated in Figs. 3 and 4. Fig. 3 is a partial sectional view illustrating that the embossed web occurs with the embossings being a mirrow-image in an imaginary plane of symmetry 23 passing through the middle of the fibrous web 15. As explaned above it has surprisingly been shown that embossings are provided on both sides even though the pressure roller 19 is smooth. Thus an impression 24 at one side of the web 15 is opposed by an im¬ pression 24 on the other side of the web 15. Areas 26 between the impression have a thickness 27 being greater than the thickness 25 across two impressions 24. The photography of Fig. 4 shows a part of a web manufactured according to the invention in which the embossing occurs as impressions and raised or non-compressed areas. The apparatus according to the invention operates in the following manner: The web 15 is led through the nip between the rollers 18,19. After having passed the nip the thickness 25 of the web between impressions 24 might be between 10 and 20% of the original thickness of the web 15. In the areas 26 between impressions the web might have a thickness 27 of approximately 2 to 3 mm whereas the thickness 25 is approximately a few tenth of a millimeter. When heating the rollers 18,19 it has shown that the product is especially soft. This effect is also surprisingly. It is believed that the momentan heating would give rise to a wapour formation occuring as a small explosion. It is believed that these small explosions would make the product more airy and thereby more soft. Besides being soft, the product would have a good hand and feel and a good drapability due to the double-sided embossing. The drapability could be compared to that of knitwears and textiles. Due to the reduced thickness 25 between opposed impressions 24 the web is provided with a large number of bending points. The large number of bending points is requisite for a good drapability. The distance between adjacent impressions could be less than two millimetres in order to achieve as many bending points as possible. Thereby an especially good drapability is obtained. When effecting the embossing it is possible to apply a modifier onto the raised areas 21 of the embossing roller 18. Thus it is possible to modify the properties of the web during the embossing process. Such modification may be provided in the form of a colouring in the impressions 24. It is also possible to use a penetrant as modifier. Such penetrant would enter into the fibers positioned between the opposed impressions 24 and affect the mechanical properties of said fibers e modifica r, <iy effected at the side of the web 15 facing the embossing roh f 18. A penetrant could e.g. affect hydrophobic fibers in a way whereby they are amended into hydrophilic fibers in the pattern or a part of the pattern of the impressions. Such modified web could advantageously be used in napkins and diapers. This effect of making so-called flow lines has been described in co-pending US Patent Application filed by the same applicant with the title "Method of producing flow lines in a sanitary product". The content thereof is hereby incorporated with refert ^.

Claims: CLAIMS 1. Apparatus for in-line processing an fibrous web in order to induce said web a double-sided embossing, characterized in that only two rollers are provided between which the web is led in order to induce the double-sided embossing, said first roller being provided with a pattern in its surface determining the form of the embossing, and that the second roller has a smooth and hard surface. 2. Apparatus according to claim 1, characterized in that said second roller is made of a cronium-plated steel roller. 3. Apparatus according to claim 1, characterized in that said first roller is provided with a pattern comprising engraved areas and raised areas. 4. Apparatus according to claim 1, characterized in that the distance between the two rollers is arranged so that no nip effect would occur on the material being situated in front of the areas of the engraved areas of the embossing roller. 5. Method for making a double-sided embossed fibrous web having a good hand and feel and a good drapability, characterized in that the embossing is effected simultaneously on both sides of the web by leading the web through a nip between two rollers one of which having a pattern of the embossing and the other having a hard and smooth surface. 6. Method according to claim 5, characterized in that the surface velocity of the rollers is between 20 and 400 meters/minute, and that the rollers are heated at a temperature between 130°C and 400°C, preferably 200 and 330°C. 7. Method according to claim 5, characterized in that portions of the web being arranged in front of the engraved areas of the embossing roller would not be squeezed during the passage between the rollers. 8. Method according to claim 5, characterized in that the raised areas of said first roller is provided with a modifier in order to modify the properties of the web during the embossing process. 9. Method according claim 8, characterized in that said modifier is a penetrant which enters into the fibers and affect the mechanical property of said fibers. 10. Double-sided embossed web of a fibrous web, characterized in that the embossing provided on one side is a mirror image of the embossing provided on the other side as seen according to a symmetry plane passing through the middle of the web.

Inventors: KROEYER KARL KRISTIAN KOBS, KROEYER, KARL, KRISTIAN, KOBS
Applicants: KROYER K K K, KROEYER, KARL, KRISTIAN, KOBS
Application year: 1994
Main classification: B31F1
IPC codes: B31F1, D04H1